Seattle weather norms...?

I have a friend who is going to Seattle for the next 45 days (from Missouri) and he is not sure how he ought to pack. based on the way Mo weather can change I'm uming that it will get cold quickly there but if anyone can give me an idea on what the weather tends to be like this time of year it may help greatly. He will be staying on the East coastline and will be there for work until roughly the start of November.